1. Field of the Invention
This invention concerns a process for utilizing solid hydrocarbon materials present in the subterranean formation and not otherwise recoverable therefrom for the purpose of heating water to generate steam and/or hot water for use in recovering viscous petroleum from subterranean, viscous petroleum-containing formations in the immediate vicinity.
2. Description of the Prior Art
Many subterranean, viscous hydrocarbon-containing deposits are not suitable for exploitation by conventional recovery techniques because the hydrocarbon materials are so viscous that they will not flow at formation temperature and pressure even if a substantial pressure differential is applied across a portion of the formation and the permeability of the formation is sufficient to permit fluid flow. For example, tar sand deposits such as those found in the western part of the United States as well as in the northern part of Alberta, Canada contain vast quantities of bituminous petroleum, but essentially no petroleum may be recovered by so called primary means because the viscosity of the bituminous petroleum at reservoir condition is in the range of millions of centipoise. Accordingly, some form of supplemental recovery process must be applied to these tar sand deposits, as well as to other subterranean, viscous petroleum-containing formations in order to recover any appreciable quantity of hydrocarbon or petroleum fluids therefrom.
A particularly promising supplemental recovery technique suitable for use in viscous oil formations and particularly in tar sand deposits is described in my application Ser. No. 481,581, filed June 21, 1974, now U.S. Pat. No. 4,006,778, which generally involves the use of air and steam in a critical ratio which produces a forward, controlled, low temperature oxidation reaction which propagates radidly through the tar sand deposits, mobilizing an appreciable quantity of viscous petroleum in the formation, and result in recovering as much as about 75 percent of the viscous petroleum present in the formation. This recovery technique is different from conventional in situ combustion processes and is more successful in application to tar sand deposits and similar viscous oil formations, because the permeability of the tar sand deposit is too low to permit application thereto of the conventional, forward high temperature in situ combustion as is practiced in more conventional oil recovery operations. Although this process results in an unusually high percentage recovery and is otherwise quite suitable for use in tar sand deposits, it does result in leaving a carbon, coke-like residue on the sand grain in the formation at the conclusion of the low temperature controlled oxidation reaction. This is in itself surprising, since although it is known that reverse in situ combustion results in the deposition of coke on the formation matrix, forward in situ combustion operations ordinarily do not result in the deposition of coke residue, rather leaving behind a farily clean sand.
In copending application Ser. No. 483,172, filed June 26, 1974, there is described a technique for converting the coke remaining on the tar sand grains at the conclusion of a low temperature controlled oxidation reaction, into a synthesis gas suitable for use as a fuel gas, as a substitute for natural gas or methane.
Most of the viscous oil recovery methods which have been previously considered for recovering extremely viscous oil such as that present in tar sand deposits, involve the injection of the thermal fluid into the formation to raise the temperature of the viscous petroleum, thereby reducing its viscosity to a level such that it will flow through permeable formation or a communication path present or formed in the formation, if sufficient pressure differential is applied to the heated viscous oil. Steam, hot water, or a mixture of steam and hot water are by far the most commonly utilized thermal fluids, because of their wide-spread availability and low cost.
The generation of steam and/or hot water for oil recovery operations is currently quite expensive because natural gas or other fuels suitable for use in generating the steam are in very short supply, and the costs thereof have escalated considerably. Accordingly, there is a substantial need for a method of generating steam and/or hot water for use in viscous oil recovery operations without the need to burn fuel which can be utilized more profitably and efficiently as a fuel for heating or other useful purposes.
Another major problem involved in generating steam is the treatment to which the feed water utilized for steam generation must be subjected before the water can be passed through a boiler or steam generator. Particulate matter suspended in water must be removed by filtration or other means in order to avoid clogging or otherwise interferring with the efficient operation of the boiler or steam generator. Minerals dissolved in the feed water must also be removed to avoid formation of scale on the boiler tubes which rapidly decreases the efficiency of the boiler, and chemical treatement techniques for removing scale-forming minerals from boiler feed water are expensive and not always entirely satisfactory. Accordingly, there is a substantial need for a means of generating steam for use in oil recovery operations using water containing excessive quantities of particulate matter dispersed therein and/or excessive quantities of minerals dissolved therein, without the expense of pretreating and conditioning the water prior to its use for steam generating.
It is an object of the present invention to satisfy at least some of these needs and at least certain preferred embodiments of the present invention as are described hereinafter below accomplish this object.